While there cannot be any kind of game without rules, enforcing them on this type of system can be hard to do. So, here are a few guidelines:

DO NOT GIVE OUT DIRECT QUEST ANSWERS. Working together to solve a quest that you have not solved is fine. Giving another player a small hint or clue when he/she is stumped is fine. Giving the answers to a quest (ie, telling someone to "go north, type xyzzyx, search drawer, stab old woman, and you're finished!") is Bad(tm). Please don't do that.

Please refrain from obnoxious or vulgar behaviour, including excessive swearing. Some people do take great offense to this. If your friends don't mind, berate them all you want.